The present invention relates generally to systems and methods for communicating data across a power distribution network. More particularly, this invention relates to a system and method for communicating data using an AC power signal to a device connected to the power line for energy management and/or control of the device.
Power line carrier (PLC) communication systems are frequently used to send data and control signals between devices connected to a power distribution network. Some conventional PLC systems communicate data by generating and then detecting disturbances in the 60 Hz AC signal that is used to deliver power to the load device. In many such prior art PLC systems, the signal disturbance is generated by using a PLC transmitter to periodically create a “short circuit” condition across the AC power line using a gated electronic switch, such as a triac. The short circuit condition is typically generated at or near a zero crossing of the AC signal. A receiver associated with the load device detects the disturbances (e.g., a “notch”) in the AC signal and decodes various sequences or patterns of such disturbances as device control signals. When the transmitter in such prior art systems is in series with the AC power line and the load device, such systems can transmit data at only a 60 Hz data rate because the disturbance can only be introduced on the positive-to negative half-cycle of the AC power signal. Also, many of the gated switches used in these prior art systems cannot be turned off by their gate signal. Thus, if the switch is turned on just after a zero crossing, the AC line will be shorted through the switch. This may damage the switch and/or disable the power line by tripping an over-current device attached to the circuit. Also, conventional PLC systems using a gated switch configuration are less efficient and must use larger and more expensive components to handle the switching losses inherent with such systems.
What is needed, then, is a PLC communication system that is easy to use on existing power distribution networks, is energy efficient, and that is smaller in size and lower in cost as compared to conventional gated switch “notch” systems.